1. Technical Field
This invention generally relates to computer systems, and more specifically relates to the measurement of processor capacity and usage in a computer system.
2. Background Art
Various methods have been developed for measuring the performance of a computer system. One measurement that is often of interest is the usage of a central processing unit (CPU), also referred to herein and in the art as a processor, by a system and by applications running on a system. CPU usage is typically reported in time units, such as processor-seconds. For a CPU that is multi-threaded, the CPU time for each thread may be monitored so the amount of time spent executing each thread may be determined.
The prior art methods for measuring CPU usage in absolute time units is appropriate only if certain assumptions are true. For example, if there is only one processor present in the computer system, and if the clock speed of the processor does not change, the amount of CPU resource used by an application may be reported directly in time units. If there are multiple processors present in the computer system, and if all of the processors are of the same type and are running at the same clock speed with the same internal circuitry enabled, the amount of CPU resource used by an application may still be reported directly in time units, because one second used on one processor means the same amount of work as one second used on any other processor in the system. Many modern computer systems, however, have configurations that do not adhere to these assumptions that allow directly comparing performance of a first processor in absolute time units to performance of a second processor in absolute time units. For example, some computer systems have different modes that allow the processor to run at different clock speeds, or to run with different internal circuitry enabled. Some computer systems include multiple processors of the same type that run at different clock speeds, or multiple processors of different types. Comparing one processor-second of a processor at one clock speed to a processor-second on a processor at a different clock speed is like comparing apples to oranges. For this reason, prior art methods of measuring processor capacity and usage are inadequate. Without an apparatus and method for measuring and reporting capacity and usage of processors of different speed and/or architecture, the processor capacity and performance in a computer system that contains processors of different speed and/or architecture will not be readily measurable.